Crystallization characteristics and chemical bonding properties of nickel carbide thin film nanocomposites

• Published in: Journal of physics. Condensed matter Vol. 26; no. 41; p. 415501
• Main Authors: Furlan, Andrej, Lu, Jun, Hultman, Lars, Jansson, Ulf, Magnuson, Martin
• Format: Journal Article
• Language: English
• Published: England IOP Publishing 15.10.2014
• Subjects: Amorphous materials; amorphous nanocomposites; Carbides; Carbon; Carbon content; Crystal structure; magnetron sputtering; Nanocrystals; Nickel; thin film coatings; Thin films; transition metal carbides; X-rays
• ISSN: 0953-8984; 1361-648X; 1361-648X
• DOI: 10.1088/0953-8984/26/41/415501

The crystal structure and chemical bonding of magnetron-sputtering deposited nickel carbide Ni1−xCx (0.05 x 0.62) thin films have been investigated by high-resolution x-ray diffraction, transmission electron microscopy, x-ray photoelectron spectroscopy, Raman spectroscopy, and soft x-ray absorption spectroscopy. By using x-ray as well as electron diffraction, we found carbon-containing hcp-Ni (hcp-NiCy phase), instead of the expected rhombohedral-Ni3C. At low carbon content (4.9 at%), the thin film consists of hcp-NiCy nanocrystallites mixed with a smaller amount of fcc-NiCx. The average grain size is about 10-20 nm. With the increase of carbon content to 16.3 at%, the film contains single-phase hcp-NiCy nanocrystallites with expanded lattice parameters. With a further increase of carbon content to 38 at%, and 62 at%, the films transform to x-ray amorphous materials with hcp-NiCy and fcc-NiCx nanodomain structures in an amorphous carbon-rich matrix. Raman spectra of carbon indicate dominant sp2 hybridization, consistent with photoelectron spectra that show a decreasing amount of C-Ni phase with increasing carbon content. The Ni 3d-C 2p hybridization in the hexagonal structure gives rise to the salient double-peak structure in Ni 2p soft x-ray absorption spectra at 16.3 at% that changes with carbon content. We also show that the resistivity is not only governed by the amount of carbon, but increases by more than a factor of two when the samples transform from crystalline to amorphous.